The invention relates to an airbag covering cap comprising a support layer and cover layer of different elasticities.
From DE 195 16 230 an airbag cover is known which consists of a molded part as the support layer and a visible covering which covers the molded part to form the cover layer. The cover layer is formed as a leather coating with a groove-like partial reduction in the material thickness into which the support layer is stretched. At this point an ideal break point is formed in the support layer and the path of the break point corresponds to that of the groove of the cover layer, i.e., the ideal break points in the support and cover layer overlap one another.
Through rear injection of the cover layer, molded into the groove, it happens that there is no material reduction which can be seen on the visible side of the sight cover and a smooth surface is produced on the visible side of the cover layer. Ornamental grooves, such as are provided in the event of weakening the upper side of the cover layer are therefore not required.
With this covering, as with other known coverings having weakened lines, it is intended that the cover tears open along the weakened lines in the event of a crash. Tearing open should however not continue over the end of the weakened lines. The drawback with the known covering described above is that further tearing beyond the end of the groove cannot be ruled out.
In order to prevent further tearing it is known to provide a small opening at the end of the groove whereby the opening-has a larger diameter than the width of the break line. This however has the drawback that the surface of the cover is broken so that the appearance is impaired.
Furthermore it is known from DE 44 24 6586 A1 to design the end sections of the break line curved so that further tearing beyond the end of the break line is likewise to be prevented.
All the known covering caps have the drawback that the opening and tearing force cannot be changed without changing the optical and/or mechanical properties of the covering cap. If the groove is indented for example to reduce the tear-open force, then the risk of further tearing at the ends is increased.
The object of the invention is to, in the case of an airbag covering cap having a smooth cover surface layer, allow the cap to tear open at a lower force without the cap continuing to tear further over the end of the proposed break line, and to change the opening and further tearing force without changing the optical and/or mechanical properties.
The airbag covering cap of the present invention includes a support and a cover layer of different elasticity with at least a tear-off line along which the airbag covering cap tears open as the airbag is deployed, wherein the cover layer is weakened in the area of the tear-off line through groove and the support layer extends into this groove, and wherein the cover layer has, adjoining the section of the support layer which extends into the groove, a section which extends into the support layer, whereby the edge between the sections of the cover layer and support layer each extend into the other layer, forming a tear-off edge.
As opposed to the known airbag covers, both the support layer and the cover layer have a reinforced section in the area of the break point. Between these two sections stretches a tear-off edge running through both layers, i.e., this tear-off edge is, seen in cross-section, substantially longer than with the known covering caps. The covering cap, in the event of a crash, tears open along this tear-off edge starting from the weakened lines above the groove in the cover layer, whereby the adhesion between the material of the support and the cover layer is slight along the tear-off edge. The reinforced sections and the extended tear-off edge on the one hand prevent the airbag covering cap from tearing open further at the end of the groove of the cover layer and on the other hand ensures in addition that the airbag covering cap tears open along the proposed line.
In one embodiment, the support layer is designed weaker in the area of the tear-off edge between the sections of the support and covering layers compared to the remaining areas and the cover layer extends into the weakened area. With this embodiment both the cover layer and the support layer are formed continuous in the area of the tear-off edge. The airbag cover tears open in the event of a crash both at the weakened points of the cover layer and of the support layer and along the tear-off edge between the two layers.
In a further embodiment, it is proposed that the support layer has in the area of the tear-off edge between the sections of the support and cover layers at least one slit and that the cover layer extends at least partially into the slit. With this embodiment the support layer is formed non-continuous in the area of the tear-off edge. Thus with this embodiment in the event of a crash the airbag cover must only tear in at the weakened point of the cover layer. It then tears open again along the tear-off edge between the support and cover layer.
In a third embodiment, a slit is likewise provided which is however bridged by thin narrow webs. The webs preferably have a width of 0.8 mm maximum and are arranged at intervals of at least 10 mm.
The thickness of the cover layer above the section of the support layer extending into the cover layer preferably increases towards the ends of the tear-off areas whereby further tearing of the cover cap can be affected.
In a further design of the second embodiment, it is proposed that the edge of the slit in the support layer is reinforced like a bead. A reinforcement of this kind is likewise possible with the first embodiment at the edges of the weakened area in the support layer. It is thereby further ensured that the airbag cover does not tear open apart from the proposed tear-open areas.
It is expedient if the tear-off edge runs inclined relative to the surface of the cover layer and the support layer in this area. By changing the inclined path and the path of the tear-off edge in cross-section it is possible to adjust the initial tearing and further tearing forces without changing the optical or mechanical properties. The tear-off edge preferably runs straight in cross-section but can also run angled in a straight line or curved.
The reduced adhesion provided between the support and cover layer at the tear-off edge can be achieved by selecting suitable materials for the support and cover layer whereby the adhesion is also reduced in the remaining areas. The reduced adhesion can also be achieved by surface treating the support layer in this area prior to applying the cover layer.
It is expedient to use thermoplastics elastomers as the support layer and cover layer.
The invention will now be explained with reference to the embodiments shown in the drawings in which: